Process for reducing the translucency of woven and knitted fabrics of polyamide fibres



United States Patent PROCESS FOR REDUCING THE TRANSLUCENCY F WOVEN AND KNITTED FABRICS OF POLY- AMIDE FIBRES Emil Knup, Arlesheim, Switzerland, assignor to Ciba Limited, Basel, Switzerland Translucent woven or knitted fabric of polyamide fibres Impregnating in aqueous bath of acid pH, containing polyvinyl ester of aliphatic carboxylic acid emulsified with anion-active dispersing agent+Metal salt for reversing charge of anion-active products Rinsing and drying impregnated fabric Calendering dried fabric at raised temperature In the process of this invention there may be used any translucent woven or knitted fabric of polyamide fibres, for example, fabrics of polyamides obtained by a polycondensation of amino-carboxylic acids or by the polymerization of amino-carboxylic acid lactams, especially of e-amino-caproic acid or e-caprolactam (Perlon), or polyamides obtainable by the polycondensation of diamines with dicarboxylic acids, especially the polycondensation product of hexamethylene diamine with adipic acid (nylon).

The bath used for impregnation contains a polyvinyl ester of an aliphatic carboxylic acid. There may be mentioned more especially polyvinyl esters of carboxylic acids of low molecular weight, that is to say, those containing 2-4 carbon atoms, for example, polyvinyl butyrate, polyvinyl propionate and especially polyvinyl acetate. If desired, there may be used mixtures of such polyvinyl esters or copolymers of vinyl esters containing different acid radicals, and also partially hydrolyzed polyvinyl esters.

The'polyvinyl ester must be emulsified in the impregnating bath by means of an anion-active dispersing agent. Among anion-active dispersing agents there may be mentioned more especially those which owe their surfaceactive properties, on the one hand, to a hydrophobic 2,982,673 Patented May 2, 1961 radical, especially an aliphatic radical, and, on the other, to an group. This. group may be bound to a carbon atom either directly, in which case it is a sulphonic acid group, or advantageously through an oxygen atom, in which case it is a sulphuric acid ester group of the formula Especially advantageous dispersing agents of the latter kind are sulphated oils, especially Turkey redoil.

It is usually also of advantage for the impregnating bath to contain at least one non-ionic dispersing agent, in addition to the anion-active dispersing agent. For this purpose there are preferably used polyglycol compounds, that is to say, compounds in which a polyglycol radical of the formula (--CH -CH O) --CH -CH -OH is bound to an amine, alcohol or mercaptan, or is bound. to the radical of an acid containing at least 8 carbon atoms. There may be used mixtures of such compounds and, if desired, other substances that enhance the dispersing action. Advantageous are, for example, mixtures of (a) Polyglycol esters of saturated or especially unsaturated aliphatic carboxylic acids of high molecular weight, for example, those containing 12-l20 carbon atoms,

(b) Polyglycol ethers of aliphatic mercaptans of high molecular weight, for example, those containing 8-18 carbon atoms and having straight or advantageously branched carbon chains, and- (c) Free saturated or advantageously unsaturated aliphatic carboxylic acids of high molecular weight.

The impregnating baths also contain a metal salt capable of reversing the charge of anion-active products. In this connection there may be mentioned above all aluminum salts, such as aluminum formate or especially aluminum sulphate.

The impregnating bath must have an acid reaction, and this is advantageously achieved by the addition of a small proportion of acetic acid.

The impregnating baths may contain other substances, for example, a small proportion of a reducing agent, which is added in order to inhibit subsequent yellowing of the textile material or of the polyvinyl ester. Furthermore, the process of this invention for reducing the translucency of the fabrics may be combined with other treatments, such as dyeing, softening, matting or an antistatic treatment.

The individual and relative proportions of the components of the impregnating bath may vary within relatively wide limits. The concentration of the polyvinyl ester depends primarily on the strength of the effect desired, and may be, for example, 1-10% calculated on the weight of the fibrous material. The concentration of the dispersing agent is advantageously adjusted in relation to the quantity of polyvinyl ester to be emulsified, in that the dispersing agent is present in at least the proportion required to form a sufliciently stable emulsion. In general the proportion of the dispersing agent required is only a small fraction of the quantity of polyvinyl ester present. The proportion of the metal salt capable of reversing the charge of anion-active products is advantageously a multiple of the quantity of the anion-active dispersing agent and is less than or at most equal to the quantity of the polyvinyl ester, for example, about ,5 to $6 the quantity of the polyvinyl ester.

The impregnating bath may be prepared by emulsifying the polyvinyl ester in water, with the aid of the dispersing agent or agents in the usual manner. It is preferable however, to dilute with water to thedesired bath strength a concentrated aqueous emulsion of the polyvinyl ester containing at least one dispersing agent, ad vantageously the anion-active dispersing agent which is essentially in the process, and to add to the diluted emulsion the further substances necessary for carrying out the process, that is to say, the metal salt, the acid and, when used, the other products mentioned above, such as the non-ionic dispersing agent.

The impregnation is advantageously carried out at a temperature from room temperature up to a moderately raised temperature, for example, a temperature within the range of 20 C. to 50 C. In order to concentrate the polyvinyl ester on the fibre, it is desirable to continue the impregnation for about -60 minutes or longer and to move the textile material in the liquid during this period. An especially suitable apparatus for this purpose is a igger.

The impregnated textile material is then dried, advantageously after being rinsed with cold water. The drying may be carried out at room temperature or a raised temperature, for example, at temperatures up to 100 C. 1

The Woven or knitted fabric so pretreated is then sub jected to a calendering treatment at a raised temperature, advantageously at a temperature within the range of 150 C. to 200 C. The pressure of the calendering rollers against the fabric is advantageously somewhat high, for example, about 30-70 kilograms per centimetre of the roller length. There may be used smooth calendering rollers or advantageously rollers having fine parallel con rugations. The effects produced by the process of this invention are distinguished by their level character and good resistance to washing.

The following example illustrates the invention, the parts and percentages being by weight:

Example 12.5 parts of an aqueous emulsion containing about 30% of polyvinyl acetate, about 1% of polyvinyl alcocentimetre of roller length. The fabric so treated is no longer translucent, and the .effect so produced has a good resistance to washing.

What is claimed is:

1. A process for reducing thetranslucency of fabrics of polyamide fibres, which comprises impregnating the fabric in an aqueous acid bath which contains polyvinyl acetate emulsified with an anion-active dispersing agent containing a sulphuric acid ester group and also contains an aluminum salt capable of reversing the charge of anion-active products, drying the impregnated fabric acid then. subjecting it to a calendering treatment at a raised temperature.

2. A process for reducing the translucency of fabrics of polyamide fibres, which comprises impregnating the fabric in an aqueous acid bath which contains polyvinyl acetate emulsified with an anion-active dispersing agent containing a sulphuric acid ester group and also contains an aluminum salt capable of reversing the charge of anion-active products, and a polyglycol compound, drying the impregnated fabric and then subjecting it to a calendering treatment at a raised temperature.

3. A process for reducing the translucency of fabrics of polyamide fibres which comprises impregnating the fabric in an aqueous bat-h acid with acetic acid which contains polyvinyl acetate emulsifiied with Turkey red oil and also contains aluminum sulphate and a mixture of'a polyglycol ester of an aliphatic carboxylic acid of high molecular weight, of a polyglycol ether of an aliphatic mercaptan of high molecular weight, and of a free aliphatic carboxylic acid of high molecular weight,

I drying the impregnated fabric and then subjecting it to hol, 0.5% of Turkey red oil and 0.1% of hydrazine hydrate are mixed with 2500 parts of water. There are then added 0.13 part of a mixture of 40% of oleic acid polyglycol ester, 40% of polyethylene glycol-tertiary dodecyl mercaptan, 15% of oleic acid and 5% of water, and 5 parts of acetic acid of 40% strength and 2.5 parts of aluminum sulphate are added. A translucent fabric of polyamide fibres is treated on a jigger with the resulting bath for 30 minutes at 30 C. The fabric'is then rinsed with cold water for a short time and dried. The pretreated fabric is then passed through a corrugated calender at 180 C. under a pressure of 50 kilograms per a calendering treatment'at a raised temperature.

4. A process for reducing the translucency of fabrics of polyamide fibres which comprises impregnating the fabric in an aqueous bath acid with acetic acid which contains polyvinyl acetate emulsified with Turkey red oil and also contains aluminum sulfate and a mixture of oleic acid polyglycol ester, of polyethylene glycol-tertiary dodecyl meroaptan and of oleic acid, drying the impregnated fabric and then subjecting it at a temperature within the range of 150 to 200 C. to a treatment with a corrugated calender under a pressure within the range of 30 to kilograms per centimeter of the length of the roller.

References Cited in the file of this patent UNITED STATES PATENTS 2,343,093 Smith Feb. 29, 1944 2,577,957 Famsworth Dec. 11, 1951 2,808,348 Harris Oct. 1, 1957 2,930,106 Wrotnowski Mar. 29, 1960 

1. A PROCESS FOR REDUCING THE TRANSLUCENCY OF FABRICS OF POLYAMIDE FIBRES, WHICH COMPRISES IMPREGNATING THE FABRIC IN AN AQUEOUS ACID BATH WHICH CONTAINS POLYVINYL ACETATE EMULSIFIED WITH AN ANION-ACTIVE DISPERSING AGENT CONTAINING A SULPHURIC ACID ESTER GROUP AND ALSO CONTAINS AN ALUMINUM SALT CAPABLE OF REVERSING THE CHARGE OF ANION-ACTIVE PRODUCTS, DRYING THE IMPREGNATED FABRIC ACID THEN SUBJECTING IT TO A CALENDERING TREATMENT AT A RAISED TEMPERATURE. 